Companion pets, such as dogs and cats, are important family members and may live to be 15, 20 or even more years contributing to the well being and mental health of the family. These companion animals longevity will best be served through good nutrition, therefore, it is important to protect the nutritional content, digestibility, and palatability of the companion pet food.
Pet foods are now generally classified into three types by their water content, namely: dry pet foods which generally have a water content of less than about 15% by weight, more particularly within the range of approximately 6-12%; semi-moist pet foods which generally have a water content of 20-40% by weight; and pet foods which have a high water content of more than 45% by weight, more particularly in the range of about 65-85%.
Pet foods having a high water content are generally sold in canned form. These canned pet foods require retorting because the high content of water is suitable for growth of microorganisms. Moreover, after can opening, the canned food should be stored in a refrigerated state because they undergo spoilage very soon. Thus the pet foods of high water content in canned form require high cost for processing in canning, and are inconvenient to store. The dry pet foods and the semi-moist pet foods are easier to package and transport, and need not be refrigerated after they are opened. They are easy to give animals, and are convenient to pet keepers.
The products of semi-moist content are unstable unless they contain extensive additives, some of which may be harmful to the animal. Due to their higher level of moisture content, they are more susceptible to microorganism growth than dry pet foods. Microorganisms which may cause spoilage are living in the products of semi-moist content because their water content is not so low as to inhibit growth of microorganisms and the temperature for heat treatment of these products is not so high as to achieve complete sterilization. Even if the products are heat-sterilized completely, they are susceptible to secondary contamination because they are packed in a simplified form. The products of semi-moist content, therefore will spoil soon if no measure is taken. The most prevalent practice of preventing microbial growth is to add some form of preservatives and/or antimycotics.
The dry pet foods contain up to about 15% moisture by weight and are the simplest to handle and store and least expensive to ship. Hard, dry pet food, while being easy to store and handle, is not as palatable as the other classes of pet food for some animals. Thus, although dry pet food may be very nutritional, in some cases it is not a particularly acceptable pet food to either the pet or the pet owner. This lower palatability is due partly to the deterioration of the pet food or overdrying of the pet food in an effort to prevent deterioration.
Two major causes of deterioration in dry pet food are microbial growth and oxidation. Both of these deterioration factors cause decreased diet palatability and decreased nutritional value. In addition, microbial growth also increases the risk of food intolerance. Some microorganisms and the toxins they produce may cause vomiting, diarrhea, and even death of animals consuming them. Problems associated with pet food oxidation also include decreased immune function and therefore increased susceptibility to infectious diseases. Cardiovascular diseases, muscular dystrophy, or degeneration and steatitis, any of which may result in death, also occur as a result of the ingestion of oxidized or rancid food. Although oxidation of commercial pet food severe enough to cause these effects is uncommon, sufficient oxidation to result in decreased diet palatability and a dry lusterless hair coat is quite common.
Methods commonly used to minimize these effects is to dry the food sufficiently to prevent microbial growth and to add preservatives to the food. Too much drying of the food however makes it hard and crumbly reducing the foods palatability to pets. Further, the heat used to dry the food increases oxidation and, if the heat is sufficient, it also decreases the diet's digestibility. Preservatives used are primarily anti-oxidants, although substances such as sugars and propylene glycol have been added to bind water making it unavailable either for microbial growth or oxidation. The major anti-oxidants used are mixed tocopherols, various acids, and synthetic chemicals such as BHA, BHT, and most commonly ethoxyquin. Ethoxyquin, which is used as an antioxidant in rubber products, is well recognized as one of the most efficient antioxidants available. Although it is allowed in pet foods, it is not allowed in foods intended for people and many question its safety for pets. A 3.5 years, two consecutive generations, study of beagle dogs showed that liver pigmentation changes and elevated liver enzymes were found in dose-dependent levels following ingestion of ethoxyquin. Pet Food Industry, 38(3):51-53, (May/June 1996). While the study concluded that the liver pigmentation was not considered critically significant and the dog's overall health did not appear to be affected, an alternative to such additives would be preferred. Whether true or not, many pet owners believe that these chemicals, particularly ethoxyquin, are harmful to their pets.
In addition to the problems associated with antioxidants, the large amount of sugar and/or sugar alcohols sometimes added, reaching as large as 20-35% by weight, is too high for usual feeds of animals and is detrimental to nutritional balance. Moreover, a high sugar content causes poor digestion in certain animals, especially old animals. Further, propylene glycol used as an antiseptic could have potentially adverse affects on the health of an animal after long term feeding of pet foods containing large amounts of propylene glycol. Accordingly, none of these measures are entirely satisfactory because of the problems of nutritional balance, the health of the animals, and palatability. Further, attempts to solve these problems have heretofore resulted in wide variations in the storagability of pet foods.
Regardless of the procedures taken to prevent dry pet food deterioration, those currently used are inadequate. In a recent study, Dr. Jim Corbin, University of Illinois, reported that "of 37 various commercial pet foods from store shelves, 43% had peroxide values in excess of 20 meq/kg of fat". Pet Food Industry, 38(1)6, (January-February 1996). Animal fat rancidity odor is easily detected by, and food palatability decreased for people at peroxidated values of 20 meq/kg or greater. Since a dog's sense of smell is 50-100 times more sensitive the people's, a much lower value is undoubtedly detected by them, decreasing the diet's palatability. This degree of oxidation also decreases the nutritional value of required essential or unsaturated fatty acids, which if sufficiently severe results in their deficiency affects. This is first indicated by a dry lusterless hair coat, a common problem in dogs receiving dry commercial dog food.
To prevent these effects, vacuum packaging in gas impermeable bags has recently been used. Although this method quite likely is effective, no results currently have been published or made available. In addition, vacuum packaging of pet foods has several major disadvantages include: costly equipment, a rate of production too slow for most manufacturing plants, and a rough poorly readable package unacceptable to many retailers and pet owners. Of three companies that have so far tried vacuum packaging, one has stopped using it and the other two have gone out of business.
Two things, water and oxygen, are necessary for microbial growth in and oxidation of a food. The present invention inhibits microbial growth and oxidation of pet food through minimizing both the water and oxygen available for food spoilage to occur. This decrease in available water and oxygen is accomplished without the use of chemical preservatives or vacuum packaging, thus eliminating the problems associated with them as mentioned above.
In addition, the present invention will provide numerous health benefits over prior art container and dry pet food combinations. In addition, the present invention provides maintained freshness and palatability as well as nutritional value of the pet food. Finally, the present invention permits prolonged shelf life and decreased production, storage and transportation costs.